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Daily Footprint, #6 – Clothing (Sustainable Textiles, Part 1)

Time to get dressed! Clothing is a huge topic so I’ll just go into one aspect here – choice of textile. Hopefully I’ll go into the other main topics in future posts: the human impact of cut-and-sew factories and the environmental impact of dyeing and finishing. Since clothing is one of our major needs in life (besides food, water and shelter) it’s worth putting some thought into which textiles are more sustainable. This helps not just with future clothing purchases but other things too, like furniture and bedding.

Types of textile materials

We can cover most of the available textiles in the following categories:

Plant-based natural fibers are composed of cellulose, the most abundant natural polymer on earth, and include cotton, flax and hemp. Flax and hemp are made from bast fibers from the stems of these plants. Natural bamboo textile can also be produced from bast fibers, but this isn’t widely practiced yet and most bamboo fabric is viscose (see #3, below).

Animal-based natural fibers are composed of protein and include wool, cashmere, alpaca, mohair, and silk.

Fibers manufactured by chemical processing of cellulose derived from plants. The two main products today are viscose made from bamboo and lyocell made from wood fiber. (A brand of lyocell known as Tencel is made from wood from sustainably-managed forests, mainly eucalyptus.)

Completely synthetic fibers, made from chemicals from the oil and gas industry include polyester, nylon, acrylic, spandex, and PVC.

Newer options that are not yet widely available in clothing include polylactic acid (PLA, made by microbial fermentation of starch or sugar) and fibers made from plant protein.

There are many factors to consider when comparing these textiles, and it can seem like an overwhelming task, but it helps to break it down by looking at one aspect at a time and then make your choice at the end. Kate Fletcher (London College of Fashion) is an authority on sustainable clothing, and I found that her books were a great place to begin researching this topic. So let’s get started by looking at the social and environmental impact of different textiles.

Textiles: Land and agricultural inputs

Synthetic fibers are often perceived as not requiring land but the impact on land, air, and ocean of the oil and gas industry needs to be taken into account (pollution from oil spills, refineries, fracking, and chemical plants).

Renewable fibers are generated directly (plant-based) or indirectly (animal-based) from sunlight and therefore normally have a lower carbon footprint (depending on agricultural inputs) than synthetic fibers.

Agricultural inputs (fertilizer, pesticides, and herbicides) are generally very low for fibers made from hemp, flax, bamboo, and trees.

Hemp and flax can be grown on marginal land (land that’s not useful for conventional agriculture, for example arid land or poor soil) and can be beneficial for soil conditioning and bioremediation. They also both produce nutritious seeds that add value to the crops.

Water and energy inputs for textiles

The chart below, compiled from a well-regarded UK reportfrom 2009, estimates the water and energy needed to make 1 kilogram of each raw (undyed) textile, including both production and processing of raw material. As with any of these impact assessments be aware that the numbers will vary according to growing region, agricultural practices and processing method.

Estimated water (in liters) and energy (in megajoules) required to make 1 kilogram of various raw textiles. (Source:Defra, UK, 2009)

Cotton isn’t looking good so far when you look at the huge water requirement together with insecticide and pesticide use. When it’s not farmed sustainably, the impact of cotton can be devastating. Take a look, for example, at this incredible BBC report on the Aral Sea – a massive body of water (once the fourth largest lake in the world) reduced to one tenth of its size over the last 50 years thanks to a former Soviet program for cotton self-sufficiency.

Nylon and viscose also have high water requirements.

Bear in mind that the amount of water used may not tell the whole story of water impact. Acrylic and hemp have similar water footprints, but the impact of the water used to prepare hemp (primarily for “retting,” separating the fibers from the hemp stalk) which can be used for irrigation afterwards may be significantly less severe than the impact on water (and air) of an acrylic plant.

Looking at the energy requirements (red bars, above), all of the petrochemical-based fibers have a larger footprint. For reference, 1 gallon of petrol contains 132 MJ of energy, so making a Kg of acrylic fiber is about the same as burning 1.2 gallons (4.5 L) of petrol.

Besides the energy input, nylon also has a significant greenhouse gas footprint as a result of the nitrous oxide produced during synthesis. This used to be completely unregulated until it was discovered that N2O is 200 times more potent than CO2 as a greenhouse gas; emissions have now been reduced by around 90% in some chemical plants.

Of the synthetic fibers, polyester (currently representing around 55% of the textile market) has quite low energy and water impacts but is non-renewable. Of the natural fibers, wool, linen and hemp are all good options so far. But there are a few other factors to consider.In the next post, I’ll conclude on textiles by looking at fiber processing and consider whether one of the most popular new textiles – viscose from bamboo – is a sustainable choice. I’ll also take a look at impact of textiles during use (and look into some key new research that looks into what happens when we wash synthetic fibers) and at the end-of-life (recycling and disposal).

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